In these years, in the field of electronic devices, it is desired to further downsize electronic devices and to improve the performance of electronic devices as well as to increase the density of circuits. It becomes advantageous not only to simply attain the functions of electronic devices only by circuitry configurations, like a SRAM (Static Random Access read write Memory) and an EEPROM (Electrically Erasable and Programmable Read Only Memory) that perform information storage operations by combining transistors, or a DRAM (Dynamic Random Access Memory) or the like that performs information storage operations by combining a transistor and a capacitor, for example, but also to implement the functions of devices utilizing the characteristics of materials themselves such as functional thin films.
Furthermore, such semiconductors are mounted for the IC chip of a credit card or the like, for example, and the technology is being diversified into a personal information memory chip for a passport or the like.
Thus, it is demanded to reduce the thickness of a dielectric material or the like used for electronic components. There is CVD for a method of reducing the thickness of such a material.
This CVD has characteristics including a film deposition rate higher than that of PVD, sol-gel, and other methods, and easy fabrication of a multi-layer thin film. Moreover, MOCVD is CVD using a compound containing an organic substance for a raw material for forming a thin film, having such advantages that safety is high and halides are not mixed into films.
Raw materials used for MOCVD are generally solid powder or liquid. These raw materials are put in a container, the raw materials are typically heated at a subatmospheric pressure and vaporized in a vaporizer, and then the materials are supplied into a thin film deposition device using a carrier gas.
FIG. 7 is a system block diagram depicting a vaporization system for such MOCVD (see Patent Document 1).
In FIG. 7, 10 denotes a supply unit that supplies a plurality of raw material solutions and the like to a vaporizer 1.
The supply unit 10 includes a gas cylinder 11 filled with a carrier gas (for example, N2 or Ar), an oxygen cylinder 12 filled with oxygen, a water storage tank 13 having cooling water stored therein, a plurality of reserve tanks 14 to 17 having raw materials for ferroelectric thin films stored therein (for example, Sr(DPM)2, Bi(C6H5)3, and Ta(OC2H5)5) for three kinds of organometallic complexes, and THF (tetrahydrofuran) for a solvent), a gas supply pipe 18 connected to the gas cylinder 11 and the vaporizer 1, an oxygen supply pipe 19 connected to the oxygen cylinder 12 and the vaporizer 1, a water supply pipe 20 and 6a distributing pipe 21 connected to the water storage tank 13 and the vaporizer 1, liquid supply pipes 22 to 25 connected to the reserve tanks 14 to 17 and the vaporizer 1, and a manifold 26 connected to the reserve tanks 14 to 17 and the gas cylinder 11.
A valve 18a and a mass flow controller 18b are provided in the path of the gas supply pipe 18. A valve 19a, a mass flow controller 19b, and a valve 19c are provided in the path of the oxygen supply pipe 19. A valve 20a is provided in the path of the water supply pipe 20. Moreover, a valve 22a and a mass flow controller 22b are provided in the path of the liquid supply pipe 22 for a solvent. Valves 23a to 25a and mass flow controllers 23a to 25b are provided in the path of the liquid supply pipes 23 to 25 for complexes. Valves 26a to 26d, an air purge 26e, and a valve 26f are provided in the path of the manifold 26. It is noted that the liquid supply pipes 23 to 25 are branched so as to connect to the liquid supply pipe 22, and provided with valves 23c to 25c, respectively.
The valve 18a of the gas supply pipe 18 is opened to control the flow rate of a carrier gas filled in the gas cylinder 11 by the mass flow controller 18b, and the carrier gas is supplied to the vaporizer 1. Moreover, for the carrier gas filled in the gas cylinder 11, the valve 26f of the manifold 26 and the valves 26a to 26d are opened and the releasing state of the valve 26e for the air purge is closed, so that the carrier gas is supplied to the reserve tanks 14 to 17. Thus, the carrier gas applies pressure to the insides of the reserve tanks 14 to 17, and the stored raw material solutions are each pressed upward in the insides of the liquid supply pipes 22 to 25 each having the tip end facing the solution, the flow rates are controlled by the mass flow controllers 22b to 25b, and then the raw material solutions are carried to the vaporizer 1.
Furthermore, at the same time, oxygen (an oxidizer) controlled at a constant flow rate by the mass flow controller 19b is carried from the oxygen cylinder 12 to the vaporizer 1.
Moreover, the valve 20a of the water supply pipe 20 is opened to circulate the cooling water in the water storage tank 13 through the inside of the vaporizer 1 for cooling the vaporizer 1.
It is noted that although the thin film forming material supply parts 27 to 30 are arranged side by side along the axial direction of the vaporizer 1 in the example in the drawing, in reality the thin film forming material supply parts 27 to 30 are radially and alternately provided using connecting parts 31 and 32 connected to the water supply pipe 20 or the distributing pipe 21 from the water storage tank 13.
Since the raw material solutions stored in the insides of the reserve tank 15 to 17 have organometallic complexes, (Sr(DPM)2, Bi(C6H5)3, and Ta(OC2H5)5), in liquid or solid solved in THF, a solvent, at room temperature, the organometallic complexes are precipitated by evaporating the THF solvent and finally made in a solid if allowed to stand.
Thus, in order to prevent the solid organometallic complexes from blocking the insides of the liquid supply pipes 23 to 25 contacted to the undiluted solutions, it is sufficient to clean the insides of the liquid supply pipes 23 to 25 and the inside of the vaporizer 1 after film deposition with THF in the inside of the reserve tank 14. The cleaning at this time is performed in the section from the outlet port side of the mass flow controllers 13b to 25b to the vaporizer 1, using THF stored in the inside of the reserve tank 14 after processing.
FIG. 5 is a cross sectional view depicting an exemplary configuration of the essential part of the vaporizer 1 (see Patent Document 1).
In the vaporizer 1 shown in FIG. 5, the vaporizer 1 includes a disperser (a dispersing unit main body) 2 to which the gas supply pipe 18 is connected, a reaction pipe 3 continuously connected to the downstream side of the disperser 2, and a heater 4 that covers the circumferential portion of the reaction pipe 3.
The disperser 2 has a gas passage 5 positioned coaxially with the gas supply pipe 18. The tip ends of the thin film forming material supply parts 27 to 30 are faced between a start upstream port 5a and an end jet port 5b of the gas passage 5 (only the thin film forming material supply parts 28 and 29 are shown as faced to each other in the drawing), so that the raw material solutions stored in the insides of the reserve tank 15 to 17 can be supplied to the inside of the gas passage 5. Moreover, the disperser 2 is formed with a cooling path 6 communicating with the connecting parts 31 and 32 for circulating the cooling water in the inside of the water storage tank 13. Furthermore, the disperser 2 includes a center rod 7 having one end positioned at the upstream side more than the start upstream port 5a of the gas supply pipe 18 and the other end positioned at the end jet port 5b, and a pin 8 that supports the tip end side of this center rod 7 (the downstream side of the gas passage 5). It is noted that the base end side of the center rod 7 (the upstream side of the gas passage 5) is supported by a pin 9 provided near the end portion of the gas supply pipe 18.
In such a configuration, a carrier gas introduction hole is cut through the inside of the disperser 2, and the center rod 7 having the outer diameter (4.48 mm) smaller than the inner diameter (4.50 mm) of the carrier gas introduction hole is provided so as to be positioned coaxially with the axis of the carrier gas introduction hole.
Moreover, the gas passage 5 is formed in cooperation with the inner wall of the carrier gas introduction hole and the center rod 7 of this disperser 2.
It is noted that the cross sectional width of the gas passage 5 is 0.02 mm. At this time, preferably, the cross sectional width of the gas passage 5 ranges from 0.005 to 0.10 mm. This is because processing is difficult when the cross sectional width is below 0.005 mm, whereas it is necessary to use a high pressure carrier gas in order to increase the rate of the carrier gas when the cross sectional width exceeds 0.10 mm.
A carrier gas is introduced from the gas supply pipe 18 from the upstream of the gas passage 5. Since the raw material solutions are dropped onto this carrier gas from the tip ends of the thin film forming material supply parts 27 to 30 positioned in the midway of the gas passage 5, these raw material solutions are dispersed into the carrier gas passing through the gas passage 5 for mist.
Thus, the carrier gas having the raw material solutions dispersed therein is issued from the end jet port 5b on the downstream of the gas passage 5 to the reaction pipe 3, the carrier gas having the raw material solutions dispersed therein, which flows through the inside of the reaction pipe 3, is heated and vaporized with the heater 4, and then the carrier gas is supplied to a thin film deposition device, not shown in the drawing.
Now, for the cooling part provided in the vaporizer 1, the cooling path 6 is formed across almost the entire length of the gas passage 5 as described above. In addition to this, for example, as shown in FIG. 6, such a configuration is known that a cooling system 33 is provided for cooling the inside of a gas passage 5 positioned in the midway to the tip end side of a center rod 7 (for example, see Patent Document 2).
It is noted that in FIG. 6, functions similar to those of the aforementioned vaporizer 1 shown in FIG. 5 are designated the same reference numerals and signs and the descriptions are omitted.